Causus rhombeatus

Rhombic night adder
Conservation status
Least Concern  (IUCN 3.1) [1]
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Reptilia
Order:	Squamata
Suborder:	Serpentes
Family:	Viperidae
Genus:	Causus
Species:	C. rhombeatus
Binomial name
Causus rhombeatus (Lichtenstein, 1823)
Synonyms [2]
List Sepedon rhombeataLichtenstein, 1823 Coluber v nigrum F. Boie, 1827 Coluber V. nigrum Cuvier, 1829 Causus rhombeatus Wagler, 1830 Naja rhombeatus Schlegel, 1837 Aspedilaps rhombeatus Jan, 1859 Aspedilaps (Causus) rhombeatusJan, 1863 Causus rhombeatus Boulenger, 1896 Causus rhombeatus var. taeniata Sternfeld, 1912 Causus rhombeatus rhombeatus Laurent, 1956 Causus rhombeatus FitzSimons, 1962 Sepedon rhombeatusElter, 1981 Causus rhombeatus Golay et al., 1993

Causus rhombeatus, commonly known as the rhombic night adder, is a species of venomous snake in the subfamily Viperinae of the family Viperidae. The species is native to Sub-Saharan Africa. No subspecies are recognized as being valid. ^[3]

Description

With an average total length (tail included) of 60 cm (24 in), C. rhombeatus is the largest member of the genus Causus. The longest individual ever recorded was a male, 93 cm (37 in) in total length, collected in eastern Zimbabwe. ^[4]

The head has a snout that is relatively blunt (i.e., more rounded than in other members of this genus), on the sides of which the nostrils are positioned. The circumorbital ring consists of 2–3 preoculars, 1–2 postoculars, and 1–2 suboculars that separate the eye from the supralabials. The temporal scales usually number 2+3, sometimes 2+4, but very rarely 2+2 or 3+3. There are 6 supralabial scales, very rarely 7. The sublabial scales usually number 7 or 10, rarely 8, and very rarely 11, 12 or 13. The first 3–4 sublabials are in contact with the anterior chin shields. The posterior chin shields are small and often indistinguishable from the gulars. ^[4]

At midbody there are 15–21 rows of dorsal scales that are moderately keeled and have a satiny texture. The ventral scales number 120–166, the subcaudals, most of which are divided, 15–36. ^[4]

The color pattern consists of a ground color that is usually some shade of brown (possibly pinkish or grayish-brown), but occasionally olive green. This is overlaid with a pattern of 20–30 rhombic blotches that have pale edges, as well as a sprinkling of black scales and oblique black bars on the sides. ^[5] Each oblique black bar is topped by one or two black spots, each with a pale centre, and strongly resembling an eye. Northern populations may be patternless, ^[4] making them difficult to identify, while in others the pale edges may be missing, the rhombic blotches may be a darker color, or there may even be a dark brown vertebral stripe. The head has a characteristic V-shaped mark that may be solid black, or brown with a black outline. ^[5] Compare this with the description of the common egg-eater Dasypeltis scabra , a species that has a colour pattern and behaviour that may be an evolutionary strategy for defensive mimicry.

Common names

Common names for C. rhombeatus include rhombic night adder, ^{[4] [5]} demon night adder, Cape night adder, ^[6] African night adder, and Cape viper. ^[7]

Geographic range

C. rhombeatus is found in Sub-Saharan Africa from Nigeria east to Sudan, Ethiopia, Somalia and Kenya, south through Tanzania, Uganda, Rwanda, Burundi, DR Congo, Angola, Zambia, Malawi, Zimbabwe, northern Botswana, Mozambique, Eswatini, and eastern South Africa to Riverdale in the Western Cape Province. No type locality is listed. ^[2]

Habitat

The preferred natural habitats of C. rhombeatus are forest, savanna, shrubland, and grassland, at altitudes of 600–2,200 m (2,000–7,200 ft). ^[1]

Behavior

C. rhombeatus is an active species that can often move relatively quickly, up to an estimated speed of 92 cm per second (3 feet per second). It is usually found on the ground, but has no trouble climbing or swimming. It is largely nocturnal, but is often seen basking in the early morning or late afternoon. However, Mallow et al. (2003) reported collecting a dozen specimens that were all active during the heat of the day. ^[4]

Most specimens are docile, seldom attempting to bite unless severely provoked. FitzSimons is quoted in Pitman (1938) ^[8] as saying that, in captivity, some specimens "become so tame that you may allow them to creep, climb and slither round your neck and inside your garments." Others, however, are more temperamental. ^{[4] [5]}

When seriously disturbed, it will put on a "ferocious" threat display that includes coiling up, inflating the body (making the dark markings stand out), hissing and puffing loudly, flattening the anterior portion of the body, and striking frantically. It may also flatten the neck and move forward with the tongue extended, much like a small cobra. Striking is done with such vigor that small specimens may lift themselves off the ground entirely. ^{[4] [5]}

Feeding

A rhombic night adder eating a toad in Mlilwane Wildlife Sanctuary, Eswatini

The diet of C. rhombeatus consists mainly of toads, but it also includes frogs and small mammals. ^[9]

Reproduction

Females of C. rhombeatus produce an average clutch of 24 eggs that require a lengthy incubation period of approximately four months. The hatchlings are 10–12.5 cm (3.9–4.9 in) in total length (tail included) and feed on tiny frogs and toads. ^[9]

Venom

Rhombic night adder bites can be serious, and in at least one bite a child had to have a fasciotomy. ^[10] The few documented bites involved pain and minor swelling with minimal necrosis. These symptoms usually disappear within 2–3 days. There have been no modern well-documented cases to back up earlier claims of fatalities due to bites from this species. ^[5] Venom yield has varied from 20 to 30 mg to 300 mg, but the venom toxicity is low with LD₅₀ values of 10.8, 14.6, >16.0 mg/kg IV and 15 mg/kg SC being reported. ^[4]

References

1. Alexander, G.J.; Tolley, K.A. (2021). "Causus rhombeatus ". IUCN Red List of Threatened Species . 2021: e.T13300985A13300990. doi: 10.2305/IUCN.UK.2021-3.RLTS.T13300985A13300990.en . Retrieved 24 January 2025.
2. McDiarmid RW, Campbell JA, Touré TA (1999). Snake Species of the World: A Taxonomic and Geographic Reference, Volume 1. Washington, District of Columbia: Herpetologists' League. 511 pp. ISBN   1-893777-00-6 (series). ISBN   1-893777-01-4 (volume).
3. "Causus rhombeatus". Integrated Taxonomic Information System . Retrieved 14 August 2006.
4. Mallow D, Ludwig D, Nilson G (2003). True Vipers: Natural History and Toxinology of Old World Vipers. Malabar, Florida: Krieger Publishing Company. 359 pp. ISBN   0-89464-877-2.
5. Spawls S, Branch B (1995). The Dangerous Snakes of Africa. Dubai: Oriental Press/ Ralph Curtis Books. 192 pp. ISBN   0-88359-029-8.
6. Brown, John H. (1973). Toxicology and Pharmacology of Venoms from Poisonous Snakes. Springfield, Illinois: Charles C. Thomas. 184 pp. LCCCN 73-229. ISBN   0-398-02808-7.
7. U.S. Navy (1991). Poisonous Snakes of the World. New York: U.S. Government / Dover Publications Inc. 203 pp. ISBN   0-486-26629-X.
8. Pitman, C.R.S. (1938). A Guide to the Snakes of Uganda. Kampala: Uganda Society. 102 pp.
9. Mehrtens JM (1987). Living Snakes of the World in Color. New York: Sterling Publishers. 480 pp. ISBN   0-8069-6460-X.
10. "Night Adder Envenomation". African Snakebite Institute Newsletter. October 2014. Retrieved 23 November 2022.

Further reading

• Boulenger, G.A. (1896). Catalogue of the Snakes in the British Museum (Natural History). Volume III., Containing the ... Viperidæ. Trustees of the British Museum (Natural History). (Taylor and Francis, printers.) London. xiv + 727 pp. + Plates I–XXV. (Causus rhombeatus, pp. 467–468).
• Branch, Bill (2004). Field Guide to Snakes and other Reptiles of Southern Africa. Third Revised edition, Second impression. Sanibel Island, Florida: Ralph Curtis Books. 399 pp. ISBN   0-88359-042-5. (Causus rhombeatus, p. 113 + Plate 15).
• Lichtenstein, [M.]H. (1823). Verzeichniss der Doubletten des Zoologischen Museums der Königl. Universität zu Berlin nebst Beschreibung vieler bisher unbekannter Arten von Säugethieren, Vögeln, Amphibien und Fischen. Berlin: T. Trautwein. x + 118 pp. + 1 plate. (Sepedon rhombeata, new species, p. 106). (in German and Latin).
• Spawls S, Howell K, Hinkel H, Menegon M (2018). Field Guide to East African Reptiles, Second Edition. London: Bloomsbury Wildlife. 624 pp. ISBN   978-1-399-40481-5. (Causus rhombeatus, pp. 574–575).

External links

• Causus rhombeatus at the Reptarium.cz Reptile Database . Accessed 2 August 2007.
• Causus rhombeatus image at FotoTime. Accessed 6 June 2007.
• Causus rhombeatus image at Cape Reptile Institute. Accessed 6 June 2007.
• Causus rhombeatus image at CalPhotos. Accessed 6 June 2007.
• Video of various species, incl. C. rhombeatus on YouTube. Accessed 13 December 2007.